Preheat the oven to 350 degrees F. .
Butter a springform baking pan and dust with flour, tapping out excess. Set aside.
In a medium bowl, sift together the flour, baking powder, and salt; set aside.
In the bowl of an electric mixer fitted with the paddle attachment, cream butter and sugar on medium speed until light and fluffy, about 3 minutes. Reduce mixer speed to low, and add egg and vanilla, beating until fully combined.
Add reserved flour mixture, alternating with the milk, a little of each at a time, starting and ending with the flour mixture. Remove from mixer. Gently fold in blueberries.
Pour batter into prepared pan; sprinkle topping over cake. Bake until cake tester comes out batter-free, 60 to 70 minutes. Transfer to a wire rack to cool 10 minutes. Remove from pan; cool 15 minutes before serving.
In a medium bowl, combine flour, sugar, cinnamon, and salt. Using a pastry blender, or a fork, cut in the butter until fine crumbs form.
Using hands, squeeze together most of the mixture to form large clumps. Can be frozen in an airtight container for up to 6 months.
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